The present invention relates to a core of a rotation apparatus, a method for manufacturing the core, and a rotational apparatus that reduce vibration.
Japanese Laid-Open Patent Publication No. 55-147964 discloses a direct-current motor that includes magnets, an armature having a core, and a commutator. The number of the magnets is represented by a product 2mn. The number of the teeth in the core of the armature is represented by a product m(2nxc2x11). The number of the segments in the commutator is represented by a product mn(2nxc2x11). In the products listed above, the sign m is an integer that is equal to or greater than one, and the sign n is an integer that is equal to or greater than three. When m is one and n is three, the number of magnet is six, the number of the teeth is seven or five, and the number of the segments is twenty-one or fifteen.
Since the motor has an odd number of teeth, the resultant of magnetic forces acting on the teeth, or the resultant of the torque vectors in the teeth is not zero. The resultant torque constantly acts on the rotor in radial directions.
FIGS. 67(a) to 67(f) show the states of the torque vector resultant in the teeth of a prior art six-pole seven-slot (seven-tooth) motor. As shown in the drawings, the motor includes a rotor 111, which is an armature. The rotor 111 includes seven teeth 110. Six magnets 112, which function as a stator, are arranged about the rotor 111. When the rotor 111 rotates counterclockwise from a position A shown in FIG. 67(a) to a position F shown in FIG. 67(f), the directions and the magnitudes of magnetic forces acting on the teeth 110 change as represented by single-dotted line arrows in FIGS. 67(a) to 67(f). The torque vector resultant T, which is obtained by summing the torque vectors ta to tg in the teeth 110, changes as represented by solid line arrows in FIGS. 67(a) to 67(f). Therefore, when rotating, the rotor 111 constantly receives a radial force that is produced by the resultant torque T, which is always above zero. This vibrates the rotor 111, or the motor.
FIG. 68 illustrates an armature 120 of a typical rotation apparatus such as a direct-current motor and the generator. The armature 120 includes a core 113 having teeth 114 and coils 115, each of which is wound about one of the teeth 114. The armature 120 shown in FIG. 68 is an inner type. If the armature 120 is used as a rotor, magnets arranged about the armature 120 function as a stator. If the armature 120 functions as a stator, the magnets function as a rotor.
To wind each coil 115 about the corresponding tooth 114, the circumferential distance W1 between the distal ends of each adjacent pair of the teeth 114 needs to be sufficiently wide. Also, to systematically and easily wind the coils 115 about the teeth 114, the space S1 between each adjacent pair of the coils 115 needs to be sufficiently wide. However, if each distance W1 is widened, the cogging torque is also increased, and thus the vibration of the rotation apparatus is increased. If each space S1 is widened, the space factor of the corresponding coils 115 is decreased, and thus the performance of the rotation apparatus deteriorates.
FIG. 69 illustrates an outer type armature 119. The armature 119 also may function either as a stator or a rotor. Magnets are arranged in the hollows in the armature 119. The magnets function either as a rotor or a stator. Like the armature 120 of FIG. 68, the armature 119 includes a core 116 having teeth 117 and coils 118, each of which is wound about one of the teeth 117.
The armature 119 of FIG. 69 has the same drawbacks as those of the armature of FIG. 68. That is, the distance W2 between the distal ends of each adjacent pair of the teeth 117 and the space S2 between each adjacent pair of the coils 118 need to be sufficiently wide. Therefore, the vibration of the rotation apparatus is increased and the performance of the apparatus deteriorates.
To solve the problems presented in the arts shown in FIGS. 68 and 69, Japanese Laid-Open Patent Publications No. 9-191588 and No. 10-4640 disclose arts in which coils are wound about separately formed teeth and then the teeth are integrated with a core.
However, since the arts disclosed in publications No. 9-191588 and No. 10-4640 require a core and a plurality of separate teeth, the number of parts is increased. This complicates the production control. Also, in the art disclosed in the publication No. 10-4640, half of the teeth are formed completely separately from a core body and the engaged with the core body to form a core. Therefore, the engaging portions of these teeth have a higher magnetic reluctance compared with the teeth that are integrally formed with the core body. As a result, the teeth have different magnetic reluctances. If this core is used as an inner rotor, centrifugal force loosens the engaging portions. This makes the magnetic forces acting on the teeth uneven and thus causes the motor to vibrate.
Accordingly, it is an objective of the present invention to provide a core of a rotation apparatus, a method for manufacturing the core, and a rotational apparatus that reduce vibration.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a core used in an armature of a rotation apparatus is provided. The core includes a first piece and a second piece. Each core piece includes a ring having a first engaging portion, and a tooth radially extending from the ring. The tooth includes an integral tooth member, which is integrally formed with the ring, and a separate tooth member, which has the same shape as the integral tooth member and is secured to the integral tooth member. The separate tooth member of each core piece has a second engaging portion, which corresponds to the first engaging portion of the other core piece. The core pieces are assembled when the first engaging portion of the first core piece is engaged with the second engaging portion of the second core piece and the first engaging portion of the second core piece is engaged with the second engaging portion of the first core piece.
A method for manufacturing a core used in an armature of a rotation apparatus is provided. The method includes preparing separate first and second core pieces, wherein each core piece has a ring, which has a first engaging portion, and an integral tooth member, which radially extends from the ring, securing a separate tooth member, which has the same shape as the integral tooth member, to each integral tooth member, wherein each integral tooth member and the corresponding separate tooth member form a tooth, wherein the separate tooth member of each core piece has a second engaging portion, which corresponds to the first engaging portion of the other core piece, winding a coil about each tooth, and assembling the core pieces by engaging the first engaging portion of the first core piece with the second engaging portion of the second core piece and engaging the first engaging portion of the second core piece with the second engaging portion of the first core piece.
The present invention also provides a rotation apparatus including a stator, a rotor, a commutator, and a plurality of brushes. The stator has a plurality of magnetic poles. The rotor has a plurality of teeth. The teeth are arranged to face the magnetic poles. A coil is wound about each tooth. The commutator is secured to the rotor and is connected to the coils. The brushes slidably contact the commutator. The number of the magnetic poles and the number of the teeth are determined such that the rotor receives no radial force.
Further, the present invention provides a rotation apparatus including a stator, a rotor, a commutator and a plurality of coils. The stator has a plurality of magnetic poles. The rotor has a plurality of teeth. The teeth are arranged to face the magnetic poles, and a coil is wound about each tooth. The commutator is secured to the rotor. The commutator is connected to the coils. The brushes slidably contact the commutator. The number of the magnetic poles and the number of the teeth are determined such that the resultant of torque vectors that act on the teeth is zero.
The present invention may provide another rotation apparatus including a rotor, which has a plurality of magnetic poles, and a stator, which has a plurality of teeth. The teeth are arranged to face the magnetic poles. A coil is wound about each tooth. The number of the magnetic poles and the number of the teeth are determined such that the rotor receives no radial force.
The present invention may also be applied to a rotation apparatus including a rotor, which has a plurality of magnetic poles, and a stator, which has a plurality of teeth. The teeth are arranged to face the magnetic poles. A coil is wound about each tooth. The number of the magnetic poles and the number of the teeth are determined such that the resultant of the torque vectors that act on the teeth is zero.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.